1. Field of the Invention
The present invention relates to a liquid discharge method in which discharge energy is applied to a liquid to discharge the liquid, and a liquid discharge head.
2. Description of the Related Art
In recent years, the market for ink jet recording devices has been rapidly growing due to the rapid growth of digital cameras and the spread of personal computers. The above ink jet recording device has features such as high-speed recording, high quality level, low noise, and recordability in various mediums, and is utilized mainly in applications such as photograph printing and postcard printing. An ink jet technology in which a predetermined amount of liquid is discharged in the form of particles to attach the liquid to the medium is also utilized in an industrial field, and the applications of the technology are increasing and varying. Therefore, further sophistication in performance of an ink jet discharge head and technical innovation have been accelerated.
In recent years, technical development of an ink jet discharge method has been advanced so as to stably discharge comparatively small liquid droplets as compared with a conventional method and reduce satellites generated behind a main droplet and having a diameter smaller than that of the main droplet. This development has been made in order to meet the needs of the market demanding higher definition images and high-speed recording and meet expectations that the technology be applied to the industrial field. The satellites generated behind the main droplet and having the diameter smaller than that of the main droplet cause numerous problems. For example, the problems include a problem caused by ink droplets that are easily influenced by air resistance, as a diameter of the droplets decreases. The problem is that satellites generated subsequently to a main ink droplet are influenced by an air current generated by the main ink droplet transmitted through the air, and are therefore shot at unexpected portions to disturb the image. Another problem is that, among the satellites, satellites having small particle diameters to such an extent that the satellites cannot be shot float as mist to cause contamination inside a recording device and failure of the device.
To reduce the number of satellites, it is proposed in Japanese Patent No. 2866848 that nozzles be substantially formed into a ring shape. It is disclosed in Japanese Patent No. 2866848 that surface tension of a nozzle portion is enlarged to satisfactorily separate ink at a nozzle hole from the nozzle portion and that the ink droplets are discharged in a state in which the droplets scarcely leave tails.
Moreover, it is proposed in U.S. Pat. No. 6,557,974 that a discharge port be formed so as to obtain an aspect ratio of the discharge port between a long axis and a short axis in a range of 2 to 5. It is disclosed in U.S. Pat. No. 6,557,974 that a large restoring force is given by a meniscus force to cut off tails of the ink droplets earlier at a position closer to an orifice plate. As a result, the tails of the ink droplets are shortened, and the number of satellites is greatly reduced.
Japanese Patent No. 2866848 discloses that a portion corresponding to the center of a ring shape to be formed is substantially required for formation of a ring-like discharge port. There is difficulty in actual manufacturing such portion.
Moreover, in U.S. Pat. No. 6,557,974, it is originally assumed that the liquid droplets have a large size of several ten pls. When the constitution of U.S. Pat. No. 6,557,974 is used in a head for discharging fine liquid droplets, a mechanism for separating the liquid droplets is not basically changed as compared with a conventional mechanism. The length of the tails is not considerably reduced. That is, the constitution of the U.S. Pat. No. 6,557,974 produces a satellite reduction effect in the case of a large discharge amount. However, when the discharge amount is as small as 10 pls or less, a sufficient satellite reduction effect is not seen.
As a result of investigation and development of the present inventors, the present inventors obtain the following finding with respect to a relation between a discharge speed and the satellites. It has been found that a length of the whole discharged liquid including the tail and the discharge speed have a correlation. As the discharge speed increases, the length of the whole liquid increases, that is, the satellites increase. With regard to the small liquid droplets in the case of a discharge amount of 10 pls or less, the tails lengthen on conditions such as a discharge speed of 10 m/s or more. The tails form the satellites having a particle diameter much smaller than that of the main droplet. When the discharge speed is as low as 10 m/s or less, the tails shorten, and generation of the satellites is inhibited. It has further been found that when the discharge speed is set to 5 m/s or less, the tail is not split, and is incorporated in the main droplet to form a single liquid droplet.
When the suppression of the satellites is only considered, it is a very effective technique to reduce the discharge speed. However, in order to improve reliability of shot precision and apply kinetic energy to the ink so that viscosity of the ink due to evaporation of a water content of the ink at the discharge port during halt can be overcome to discharge the ink, the reduction of the discharge speed cannot be an effective solution to the problem.